Seatback/Seatbottom Gearbox Replacement, e32

2-23-2002

If you've already done the "Cable Fix" and still have seat
twist/tilt problems, & if there's a clicking or
crunching/grinding noise when powering the seat position(s), then
one or more wormgears are probably stripped in either the left or
right seat gearbox:

Right side shown, BMW part no. 52 10 1 964 176 (left side = 52
10 1 964 171). I bought a used gearbox from Gibby, ebay username
"gauction-pro". Great seller & always has lots of
e32's that he parts out & sells piecewise at good prices, I
highly recommend him. I hate to think what the dealer charges for
a new gearbox.

Good used gearboxes are also available at Vines
& perhaps numerous other salvage yards.

To replace, remove the headrest (it comes out if pulled
straight up firmly). Remove the 2 screws on either side of the
seatback:

The back panel of the seatback will pry off from the bottom
edge, pull straight out & lower a few inches to clear the
upper clips:

Snip the cable ties for the headrest motor power cable &
unplug the socket. The seatback will now unlatch by pressing the
bottom latch levers downward. I found it was easier to unhook the
tops of the springs:

The seatback will lift off of the arms on either side &
come clear off.

Slide the seat bottom forward to expose the Torx head bolts on
the rear seat rails & remove them, if you don't have a Torx
socket (E60?), a 7/16" or 11mm 12-point socket will work.
Remove the seatbelt lug & wire cable underneath the seat (see
"Seatback Twist" section for more
details).

With the seat bottom removed, peel back the leather from the
side to expose the mounting screws & circlip for the gearbox:

Remove the gearbox cables from the motors (again, refer to the
seatback twist section) & snip the
cable ties holding the drive cables to the seatbottom. Chuck the
end of the rear cable with a cordless drill & drive the
seatback bracket to the fully reclined position. Pry the gearbox
free from the side of the seatframe & pull it out from the
back of the seat:

Remove the push-on retainer clip on the plastic wire harness
clamp which is on a stud toward the rear of the inside of the
gearbox:

The gearbox on mine had a stripped nylon gear on the recline
wormgear:

For this particular design, a good wormgear should have
straight teeth. Mine is obviously worn round & not making
good engagement with the worm.

If using a used replacement gearbox, now's a good time to do
the "cable fix" if it needs it, while the gearbox is
out on the bench. The motor end of the drive cables should extend
about 1/2" to 5/8" beyond the end of the outer sheath
when the other end is fully inserted into the gearbox socket.
Also, it wouldn't be a bad idea to open the cover on the
replacement gearbox to inspect the nylon gears for wear &
grease the geartrain with vaseline.

As usual, assembly is reverse order of disassembly. There's a
shim that goes between the gearbox & the seat frame on the
large stub shaft which has the circlip & clock spring.
"Glue" the shim in place with some heavy grease,
otherwise it likes to get caught in the circlip groove &
keeps the stub shaft from going back into the seat frame all the
way. There is also a small aluminum guide sleeve for the curved
rack gear for the rear seat height adjust drive which goes on a
post next to the pinion gear.